1. Field of the Invention
The present invention relates to an electronic musical instrument which can provide an external or internal, electronically-operative sound source to synthesize musical tones, and, more particularly, to an electronic string instrument provided with a fingerboard and a plurality of strings, a chord discriminating apparatus incorporated into the electronic string instrument and a chord-using apparatus such as an automatic or manual accompaniment unit.
2. Description of the Related Art
In the field of electronic musical instruments, the keyboard instrument is the most successful on an industrial and commercial basis. The input technology for use in ordinary electronic digitized machines such as an electronic typewriter, a personal computer and an electronic calculator, has contributed to improvements of a keyboard serving as a main controller of keyboard instruments and input technology associated with such a controller. The MIDI (MUSICAL INSTRUMENT DIGITAL INTERFACE), which is then most popular of musical instrument interfaces, appears to be mainly developed for digital keyboard instruments. Today, there are a variety of electronic keyboard instruments available on the market, some for professional uses, some for amateurs and some as toys for children.
Needless to say, to sufficiently master one instrument, whether it is a traditional instrument or an electronic musical instrument, generally, one has to practice considerably and requires a considerable time for it. The first thing to be learned by learners who use a musical instrument for the first time would be the basic operation of the instrument. Learners may already have sufficient musical feeling, but usually find it difficult to express music through musical instruments in which they are not experienced. It is therefore very advantageous to provide aiding or helping tools for those with less experience to help them show their musical expressions or to help learners develop a musical feeling.
One of such tools has already been devised as a simplified chord designation technology or an automatic accompaniment technology in the field of electronic keyboard instruments. This tool is disclosed in a number of documents. For instance, U.S. Pat. No. 4,353,278 discloses a chord discriminating apparatus which discriminates a chord from key operation data defined by simplified finger positioning and the subsequent key operation (striking or pressing keys) done with respect to a keyboard provided on the left side of a electronic keyboard instrument. According to the logic of the chord discrimination, the root of a chord is specified by that of two operated keys which generates the lowest tone or highest tone, and the type of the chord is determined by the type of the remaining key (black key or white key). Another chord discriminating apparatus for use in an electronic keyboard instrument is disclosed in U.S. Pat. No. 4,499,807, in which when one key is operated, the pitch of the key specifies the pitch of the root and a major is designated as the type of a chord, and when two keys are operated, a minor is discriminated as a chord type and the pitch of the root is determined by the pitch of one of the keys. When three or more keys are operated, a seventh chord is discriminated as a chord type and the root is defined by the key with the highest or lowest note. U.S. Pat. No. 4,217,804 discloses an electronic keyboard instrument which automatically plays an arpeggio in accordance with key operation data from a keyboard and an arpeggio pattern. This instrument comprises mean for assigning pitch order attributes to the individual pitches of a plurality of keys, and arpeggio pattern generator means for generating the pitch order attributes at timings at which individual musical tones are generated. The generated pitch order attribute data of an arpeggio pattern is decoded in accordance with the pitch order attribute and pitch of an operated key to be a pitch representing a specific frequency, and a musical tone having this decoded pitch will be generated and sounded. Therefore, this structure cannot generate a pitch other than what is specified by an operated key. An automatic accompaniment unit for use in a keyboard instrument is also known, which comprises pattern generator means for generating pitch interval data from a root (a pitch relative to the root) at a generation timing of each musical tone. This unit further comprises chord discriminator means for discriminating the root and type of a chord from operated keys on the keyboard. The pitch interval data from the tone generation control means generator means of the is sent to decoder means where it is corrected in accordance with the discriminated chord type and is combined with the root of the chord to be a pitch having a specific value. A musical tone having this pitch will be generated from a sound source.
It should be noted that the above techniques have been proposed and developed in association with a musical instrument having a keyboard, i.e., a musical instrument having an array of keys which are basically arranged in a linear pitch array and are struck or pressed. In general, it is considered difficult to apply the principles of such techniques to musical instruments which apparently differ from the keyboard type in, not only structure but also characteristics and modes of musical performance.
It seems useful to briefly discuss the characteristics, history and state of the art of an electronic string instrument.
As compared with electronic keyboard instruments, the history of electronic string instruments is shorter although the root of ordinary string instruments goes back to ancient times. Analog-operative "electric" guitars are very successful at modern times. String instruments differ from keyboard instruments significantly in playing method. With regard to a guitar, for instance, musical tones are generally generated by plucking or strumming one or more strings. The pitch of a tone is basically determined by the operation position pressed on the associated string on a fingerboard with a finger. In other words, each tone is determined and generated by the positioning of a string with the left fingers and plucking or strumming of the string with the right fingers. This is in contrast to what is involved in keyboard instruments in which one or a plurality of keys are selected and struck or pressed to generate associated tones. Due to the structural advantage, most string instruments are portable and are typically held by a player while playing a musical piece. This produces a feeling of integration between a player and a string instrument, which is not the case with the use of keyboard instruments.
Although the history of electronic string instruments is relatively short, various propositions have been made to digitize or computerize string instruments. Great efforts have been made particularly to improvements of an input or sensor device associated with strings and a fingerboard which are main play controllers of a guitar type string instrument or a signal processor associated with such an input or sensor device. Typical performance control inputs, which are detected and evaluated by an electronic string instrument and are used for a sound source of a synthesizer, are the position of a string pressed on the fingerboard or the operating length of a vibrating string or its equivalent pitch, the time of string plucking (or strumming) and sometimes the intensity of the string plucking. For instance, U.S Pat. No. 4,468,999 teaches a string/fret detecting apparatus for use in an electronic guitar, in which a plurality of metal strings are sequentially and periodically driven by a string driver. Conductive frets on the fingerboard are sequentially and periodically scanned by a fret scanner, which receives an electric signal of a string through a fret in contact with the string and discriminates the fret by a differential system. The string driver drives one string at a time in accordance with the value of a string counter, so that the string in contact with the discriminated fret is specified by the string count attained at that point of time. U.S. Pat. No. 4,658,690 also discloses a string-driven type string/fret position detecting apparatus. In this apparatus, a fret comprises a plurality of mutually-insulated, conductive segments arranged in such a way that adjacent fret segments partially overlap each other across the fingerboard (while maintaining the insulation). This string/fret position detecting apparatus can detect a plurality of string/fret positions, and these strings extending on the fingerboard are separate from the strings (trigger strings) which are disposed on the body of a string instrument and are to be plucked or strummed. According to the guitar type electronic string instrument disclosed in U.S. Patent application Ser. No. 069,612, filed Jul. 7, 1987, a matrix array of pressure-responsive fret switches are embedded in the fingerboard body. Each fret switch is associated with each string extending on the fingerboard and is provided between adjacent frets thereon. The fret switch array is scanned by an array scanner or a program and an activated fret switch or the operation position of each string pressed on the fingerboard is detected. U.S. Pat. No. 4,723,468 discloses an apparatus for detecting string/fret positions and the operation lengths of strings utilizing ultrasonic waves. An ultrasonic wave generator operative by a pulse is provided at the bridge of the strings and transmits an ultrasonic pulse. The transmitted ultrasonic wave is reflected by the fret on the fingerboard which is in contact with a string, and the ultrasonic echo is returned to the bridge through the string in the opposite direction and is received by an ultrasonic wave receiver provided at the bridge. The time between the transmission of the transmitted pulse and reception of the received pulse, i.e., the time required for the ultrasonic wave to reciprocate the operation length of the string, is measured and the associated, activated fret is specified. U.S. Patent application Ser. No. 112,780, filed Oct. 22, 1987, corresponding to U.S. Pat. No. 5,018,428 proposes a string/fret detecting apparatus of a pitch extraction type, which extracts a pitch from a signal from an electromagnetic pickup of a string. This pitch extracting apparatus comprises an analog circuit and a digital signal processor which is controlled by software (a pitch extraction algorithm). The analog circuit detects the zero crossing point, peak, etc. of the picked-up signal and sends the detection results to the digital signal processor. In accordance with the pitch extraction algorithm, the digital signal processor finds effective zero crossing points (whose interval corresponds to the pitch or basic frequency of string vibration) and measures the time between the effective zero crossing point to attain a pitch.
French Patent FR8606571; FR2598-017-A discloses a string-plucking or violin type electronic string instrument. According to the embodiment disclosed, a strength gauge for detecting the bow pressure with respect to strings is adhered to the flexible stick of the bow. The hair of the bow is constituted by a bundle of 50 silicon carbide wires having 1000 .OMEGA./cm and is applied thereacross with a DC voltage of about 5 V. Each string is conductive and serves as a cursor for a potentiometer constituted by the bow hair. When the hair contacts a string, a voltage indicating the contact position (instantaneous position of the bow) is formed on the string. Resistive tracks of carbon are embedded in the fingerboard in association with the individual strings, and a DC voltage of about 5 V is applied across each track. For each track, a conductive wire which selectively contacts the track when pressed, is disposed. The tracks serve as the potentiometer and the conductive wires serve as the cursors. When strings are pressed against the fingerboard, therefore, signals representing the pressed positions are formed on the conductive wires. These signals, which include a signal representing the bow pressure from the strength gauge with respect to the strings, a signal from a operated string that represents the instantaneous position of the hair with respect to the string, and a signal from a conductive wire representing the position of the string pressed against the fingerboard, are utilized to control a synthesizing sound source.
Of course, these efforts and propositions concerning string instruments generally relate to evaluation of performance control inputs in "electronic" string instruments, and their objectives are essential to actually realize the potential of a sound source for electronically synthesizing musical tones in response to properly evaluated tone parameters. However, there are still important aspects in electronic string instruments which should be developed, and which are concerned with the technique for providing aid and help to players, particularly those who do not have enough experience in string instruments. This technique is what the present invention is directed to. Regretfully, in the field of electronic string instruments, there are very few documents published which are concerned with the play-aiding, field. One of the documents is U.S. Pat. No. 4,295,402, issued Oct. 20, 1981. The disclosed technique relates to correction of chord designation including an error in an electronic guitar. A fret position detector detects operation positions (a set of operation positions of string/fret operation positions) on a fingerboard with frets, which are determined by (erroneous) fingering done for chord designation with respect to the fingerboard. The set of operation positions is converted into a set of associated pitches, each of which is expressed by one of 12 bits so that all the pitches can be set within one octave. The converted data is then input to a chord/root detector, which has a plurality of matching or correlation filters and counters provided for different chord types. Each correlation filter is first supplied with 12 bits Si representing the set of pitches from the fret position detector. During a checking process, these 12 bits Si are sequentially circulated so as to move a reference bit position or a root from C to B. The correlation filters further receive reference pitch data representing chord types, as filter coefficients, which are equivalent to 12 bits Ri that make the bit positions of the chord members to be "1." The outputs of the correlation filters are given by ##EQU1## The outputs (correlation values) are measured by the correlation counters. The type of a chord is specified by that correlation filter which has given the greatest correlation value, and the root of the chord is specified by the reference bit position given at the point of the maximum correlation value. In other words, this structure is based on the signal theory concerning the signal-to-noise ratio. However, the disclosed technique is not utilized for a purpose of discriminating a chord from the operation positions on the fingerboard formed by "simplified" fingering for chord designation. The latter technique is suggested in Japanese Patent Disclosure No. 63-210893, according to which each chord type is assigned to each string and the root of each chord (from C to B) is assigned on each fret on the fingerboard. A chord is specified by pressing one point on the fingerboard. Accordingly, a positioning detector means detects one operated string/fret position. The type of a chord is discriminated from the string data at the operation position from the positioning detector means, and the root of the chord is discriminated from the fret data at the operation position. With the above arrangement, since the pitch on the same fret is assigned to every string, most players who enjoy playing traditional string instruments, more or less, would feel it unnatural. Another example is disclosed in Japanese Utility Model Disclosure No. 63-128596, whose grantee is the same as the present application. In this example, separate regions on a fingerboard with frets are used respectively as a chord type designating region and a root designating region. According to one embodiment disclosed in the document, the region or track on the fingerboard which is associated with the sixth string defines the root designating region and those tracks on the fingerboard which are associated with the first to fifth strings define the chord type designating region. This arrangement has a shortcoming similar to that of the previous example.